Treatment of iron sulfate liquors



i atentecl Apr. 20, 1948 QFFICE;

TREATMENT-demon sotrrrmroiioits' Louis N. Allen; J 1Q, Short Hills} N;J1, and walter K. Zahray, Bronx, N. Y., assigfiors t'ocheniical(ionstruotion' Corporation; New York-,- N. Y,- a

corporationpf Delaware fiofirawirig. iirpiication March 21, 1946,

Serial'No. 656,174

4 Glaims. (01. 23-126) This invention relates to a method for the"treatment of waste iron sulfate liquor's contain irig free sulfuricacid, such as' spent pickle liquors encountered in steel mills and'acid' ferroussulfate solutions: obtained as byproducts in thenianufacture of titanium dioxide pigments from: ii menit'e. It is a principalobject of the invention to provide a method of' separating aconcentrated.- ferrous sulfate sludge from" these and'similar waste ironsulfate liquors that can be used for water purification, for" the" manuifacture of iron oxide" pigments; orfor rbastin'gunder conditionssuchas to'fo'rm-"a sulfur dioxide gas that can be reconverted tosulfuric acid by the contact processl We havefoiindtliatfrom about 40%to about 100% of the iron contained in spent iron sulfate liquors of theabove type can be separated in the form of a concentrated ferroussulfate monohydrate sludge by subjecting the liquors to a settlingprocess while maintaining the temperature between about 100 C. and about175 200? C., provided certain conditions are observed. These conditionsare, first, that the free acidity of the liquors is reduced to a pointwhere the pH at' ordinary" tempe atures is not below 2, and secdr'fdly;that Substantially all the" iIOfi iii the liquors is present' in theferrouscondit'ion. When" these conditions are maintained, we findthatthe sludgeshavingi' a ferrous sulfate content on the orderof 25-35%FeSir can be obtained from- 1U-15% FesOi liquors by gravity separationfor periods of about -20 minutes. These sludges solidify on cooli'ng-tomasses of ferrous sulfate heptahydrate which can be dried in tr currentof hot gases and used for water purification. Alternatively, the sludgescan be further dewatered by filtering, water evaporation or otherwiseand sub'jected to roasting 'in admixture" with about 10-14% carbon toproduce a 5-7'% S02 gas and an iron oxide that-iswell suited for use inblast furnaces.

Whenthe process of our invention is applied tc'straight ferrous sulfateliquors containing little or no ferric sulfate; such as those obtainedin titanium dioxide pigment manufacture, the sulfiii'ic acid can be"neutralized" by any suitable means. Under these circumstances relativelycheap neutralizing agen'ts such as limestone or calcium oxide orhydroxide-may be used to obtain a pI-I higher than 2, or sodiunihydroxide or carbonate may be employed if a pure ferrous sulfate productis desired. In treating spent pickle liquors, however, which containconsiderable quantities of ferric sulfate, a reducing agent 2 must beemployed, this r ason we greedy prefer to treat these liquors with"aqii'e'tal above hydrogen in the electfdmotive' force serie of ele mentsand preferably with: finely divided ifoh, since this treatnierit willsimult riebuslyinu or reduce the acidity if the liquors fionier eesserydegree and a-lso reduce suh'stantiallyallf the-ferric sulfate to theferrous condition. Prefera ly the iron is added in amounts ifr ex'ifss'of" those necessary to react Witl'i' all the free s'iilfifrid" acidpresent, and-theliquo'rs fiiaybeh'e'ated to celer; ate theneutralization ofthe" free sul'fi As is noted above, the" liquoifsfiiiist beh to temperatures in excess" of CT, and preferably toaboutwaif- C.-iriordei to'briiig about the separatiomof' the ferrous" smra'teas' aT s udge. If desired, the-iron uitars 1 disrepair be neared tothese temperatures idr'td the addition of the iron or other acidneiitralizifigl agent, but we prefer to carryouttiie abidfie'utraliziiig step at a lower temperature sgph'itm open reactionvessel may be used. This permits the escape of the hydrogen" liberated"during the acid neutralization. The neutralized and reduced liquors,arethe'ri heated in a-press-u'reve'ssel to'the desired settlingtemperature and" maintained at this temperature while the" ferroussulfate" sludge is settled out and Withdraw-n 2- The not super natantliquor can ther'i -bepassed in heat exchange with fresh ironsulfateliquor in order 't'o recoverpart of its heat conteritif desired.U

From the foregoing it is apparent that the process of ourinventionconsists essentially in the steps of first reducing the freesulfuric acid contentof waste sulfuric acid-liquors to' about 0.1 orless, corresponding to apI-I of 2 or more, and reducing any ferric irontliaii'mayb e present to the ferrous condition, err the liquors at about100 200 65 under settling conditions. In order to prevent'exc'essweerratum tior'i'it'is usually au'visebleaocarryputthesettnng step" in aclosed vesser undefthe autog'enicpressure produced by the heating and byany-hydrogen evolution that may'takeplabe, and a2 pr'es- Sure vesselequipped withsteam cons-ari with a Dorr thickenerin melower nortion isvery effective for thi'sfpurpose. Preferably theves'sel is equipped witha bottom outlet so the separated sludge may be on while maintainingsubstantially the" same" temperature and pressure conditions that wereused the settling. The sludge may be further dewatered if desired byinjection into a chamber maintained at normal or reduced pressure, sothat a part or all of the free water is removed by flash evaporation.Alternatively, the water may be removed by filtration, although thisprocedure is less desirable since a heated pressure filter or centrifugewould be necessary to prevent the sludge from waste iron sulfate liquorscontaining free sulfuric acid when the acidity of the acid isneutralized to a pH not lower than 2 and when substantially all the ironis in the ferrous condition. When ties of free sulfuric acid. Solutions4-8 are examples of the results obtained at different operatingtemperatures when sufficient iron is added to convert the liquors to 'areduced and substantially acid-free condition. Solution 9 illustratesthe adverse effect of ironoxi'de when used as a neutralizing agent.

From these results it is evident that substantial recoveries of ferroussulfate are obtained from immediately setting up as a mass of copperasthese conditions are maintained at 53% recovery crystals. can beobtained at 125 C. and a 97% recovery The process of our invention willbe further at 175 0.; therefore it is usually unnecessary to illustratedby the following specific example, a exceed the latter temperature.However, temwhich shows by experimental evidence the results peraturesup to 200 C. or even higher may be emobtained under various operatingconditions. It 10 .ployed in some cases, as when more highly conshouldbe understood, however, that although centrated solutions are employed,and are inthis example may describe certain specific fea- .cludedwithinthe scope of the invention in its tures of the invention, it isgiven primarily for .b'roader aspects. purposes of illustration and theinvention in its What'we claim is: broader aspects is not limitedthereto. 1. A method of treating a ferrous sulfate liquor containingfree sulfuric acid which comprises Example adjusting the acidity of saidliquor to a pH with- Ferrous sulfate liquors having th compositions n hrange of m 2 to about and reducing :given in the following table weresynthesized by any fPrnc iron a may be present to the ferrous dissolving73 grams of copperas in water. To common addmg the liquor a metalfibwe:some of these solutions 27 grams of ferric sulfate hydrogen 1n 2electfomotive force genes of were added, in order to approximate thecontent elements heftmg 1 to a temperature of or a representative steelmillpickle liquor, and least 100 Co sublectmg he liquor to a set-:solutions 3 to 12 were acidified by adding 12 grams Dr 0065s l saidelevated temperature and 96% ulfuri acid Finely divided iron was therebyseparating therefrom a ferrous sulfate added to solutions 4 to s andmill scale to solud 'tion 9 and these liquors were heated withagitaaccor (1128 to claim 1 m which the :tion until the evolution .ofhydrogen was subhquollsaspent p k eliquon. stantially complete. Theywere then heated in A meth9d accrdmg 3001mm 2 in which the :2. pressurevessel to the temperature indicated 30 added metal 15 Ironand allowed tostand for 10-20 minutes, after A to claim 3 m which the which thesupernatant liquor was drawn off from tenlpera'ture 1s mamta'med between125 and the settled Sludge While maintaining the same 1'75 0. duringseparation of the ferrous sulfate temperature. The liquor was tested forpH and Sludgefree sulfuric acid and the liquor and sludge were LOUISALLEN analyzed for ferrous and ferric sulfates. The fig- WALTER ZAHRAY-ore for Per cent FeSO4 Recovery gives the per cent of total iron sulfatein the liquor (including REFERENCES CITED that formed from the ironadded as such or as The following references are of record in the millscale) that was recovered in the sludge. 40 file of this patent:

Composition of Liquor, Grams Supernatant Liquor Sludge N0 3gp Per cent Fs H so Add d P P P w (94%; 1.222311. 22.21 DH ear 222581;. g

150 7a 27 None None 169 12.1 2.8 2.1 14.6 5.0 22 150 73 None None None196 5.4 None 3.3 16.8 None 68 150 V 73 None 12 None l84 13.2 None 4.11.8 14.7 None 13 150 73 None 12 8.6 184. 4.9 None 0.1 4.2 28.4 None 8373 27 12 17-9 157 23.2 None 0.1 4.3 26.9 None 53 70 73 None 12 7.3 23.6None (0.1 4.1 23.8 None 6 150 7a 27 12 is 157 8.2 1.2 0.1 2.1 27.7 2.2so 73 27 12 18 157 2.0 None 0 3.5 36.5 None 97 150 73 None 12 184 2.91.0 3.0 0.7 12.0 1.0 30

1 30 grams of Blooming Mill Scale were added. This scale contains Fe,FeO, F620), and Fe1O1.

A comparison of solution 1 with solution 2 UNITED STATES PATENTS showsthat substantial quantities of ferric sulfate j interfere with theseparation of ferrous sulfate gg g g i a1 u g sludges, even insulfuricacid-free solutions. On 6 ,2005120 Whetzel et a1 June 1935 theother hand, small quantities of ferric sulfate 0 up toabout 3% areapparently harmless, as in OREIGN PATENTS v j 7 Number Country DateSolution 3 shows that very low recoveries are 365981 Great Britainqantzs 1932 obtained in the presence of substantial quanti- 65 g OTHER.REFERENCES table 80. Published in NewYork by I Van Nos- A trand Co, Inc.

